Preparation and characterization of biochar-iron oxide-palygorskite composites for uranium(VI) removal from aqueous solutions

Removal of uranium from acidic aqueous solution by natural fluorapatite

Mesoporous silica materials were synthesized using tetraethoxysilane (TEOS) as precursor and liquid crystals (LCs) formed in mixtures of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) with additions of NaBr and 1-hexanol as templates. For this purpose, the formation of LCs in the mixtures under different conditions was first studied. It was found that the additions of 1-hexanol and NaBr can synergistically weaken the electrostatic interaction between CTAB and SDS and promote the growth of the ordered assemblies, leading to the significant expansion of the LC phase areas in both SDS excess area and CTAB excess area, respectively. The effects of 1-hexanol concentrations, surfactant concentrations, and pH values on the phase diagram and hence the structures of LCs were subsequently studied. These LCs are well-structured templates for the syntheses of mesoporous silica materials that were characterized using nitrogen adsorption/desorption analysis and scanning electron microscopy (SEM). It was shown that 1-hexanol played an important role in the formation of LC templates and hence effectively improved the specific surface area and order of mesoporous materials. The BET specific surface area was high up to 937 m2/g and the average pore diameter increased to 2.5 nm when the total concentration of CTAB and SDS was 0.2 mol/L, the molar fraction of CTAB in the mixture was 0.82, the concentration of 1-hexanol was 0.4 mol/L, and pH value was 2. These studies shed light on the syntheses of mesoporous materials with large specific surface area and highly ordered structure for multiple applications.

In this study, the removal of uranium from aqueous solutions by diatomite earth (Kieselguhr) fine particules has been investigated. Diatomite earth is an important adsorbent material in chromatographic studies. Uranium adsorption capacity of four different types of diatomite was determined. The adsorption of uranium on the chosen diatomite sample was examined as a function of uranium concentration, solution pH, contact time and temperature. The adsorption of uranium on diatomite followed a Langmuir-type isotherm.

A novel chelator diethylenetriaminepentaacetic phenylenediamine (DTPAA) was successfully synthesized using p-phenylenediamine and diethylenetriaminepentaacetic acid. The as-synthesized DTPAA was covalently bonded to a supporting matrix of graphene oxide (GO), and a composite material (GO-DTPAA) was obtained. The structure of GO-DTPAA was characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The morphology was observed using scanning electron microscope (SEM) and Raman spectroscopy. The adsorption of uranium(VI) from aqueous solution was investigated using GO-DTPAA via batch experiments. Results indicated that GO-DTPAA was a highly efficient absorbent for the removal of uranium (VI) from aqueous solution at pH 6.5. Kinetics and adsorption isotherm investigations revealed that the adsorption process was well-fitted by pseudo-second-order kinetics and by the Langmuir isotherm. The adsorption capacity of GO-DTPAA was as high as 485.0 mg·g−1 at 298.15 K, which was far greater than that of pristine GO (97.3 mg·g−1) at the same temperature.

The removal of uranium (VI) from aqueous solutions onto natural sepiolite

Potato peel (PP) as bio-residue from the food processing industry used as novel uranium adsorbents, applied for studying the adsorption of uranium from aqueous solution. In batch studies, the adsorption of uranium (U, VI) from aqueous solutions onto PP was examined. From FTIR, PP represented function group (carboxyl, amino, and hydroxyl) on its surface lead to improve its adsorption. Moreover, Chloride media's showed the best adsorption efficiency for U (VI) reached up to 95.75 by PP. Also, the adsorption was studied at various temperatures, uranium concentrations, times, and pH values and the results showed that pH 4 was the best for uranium adsorption onto PP. The adsorption of uranium increased and reached to equilibrium times at 60 minutes with adsorption capacity of 19.25 mg/g. Furthermore, the bio-sorption process fit the Langmuir isotherm model well, and the kinetics were described by a pseudo-second-order rate equation, specifically. FTIR, ESEM-EDX, XRD, particle size, and zeta potential techniques were used to confirm the uptake of uranium by PP. Ultimately, the results of this study showed that PP may be a practical, quick, affordable, and effective way to extract uranium from an acidic monazite mineral aqueous solution.

The study deals with the uranium removal from a raffinate solution (nitric acid waste solution from the production of uranium yellowcake) using an extractant-impregnated material. A polyamide sheet (Nylon 6,6) was impregnated with trioctylphosphine oxide and tested for uranium removal. The factors affecting the impregnation process, namely, extractant concentration, impregnation time, volume/mass ratio, impregnation temperature, and diluent type were studied. The effect of the initial uranium concentration, adsorption temperature, contact time, and pH on the uranium adsorption on the prepared sheet was also studied. The uranium adsorption behavior was described using adsorption isotherms.

Polyvinyl alcohol/tetraethyl orthosilicate/aminopropyltriethoxysilane (PVA/TEOS/APTES) nanofiber membrane was prepared by the sol–gel/electrospinning method and its application for adsorption of uranium from aqueous solutions was compared with PVA/TEOS/APTES membrane prepared by sol–gel/casting method. The prepared membranes were characterized by Fourier transform infrared, scanning electron microscope and Brunauer–Emmert–Teller analysis. The surface area of electrospun and casting hybrid membranes obtained were 153 and 282 m2 g−1, respectively. Experiments were carried out to investigate the influence of different sorption parameters, such as pH, contact time, initial concentration and temperature in a batch system. Results indicated that the pH of 4.5 and high temperature (45 °C at studied condition) proceeded earlier than the adsorption of uranium ions onto the both of prepared membranes. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were applied to describe the equilibrium data of uranium to the prepared membranes at different temperatures (25–45 °C) and the kinetic data were analyzed by pseudo-first-order and pseudo-second-order kinetic models. The maximum adsorption capacity of uranium ions onto the PVA/TEOS/APTES hybrid nanofiber membrane was found to be 168.1 mg g−1 with the optimum pH of 4.5 and at the optimum temperature of 45 °C which is more than five-fold greater to that of uranium sorption onto the PVA/TEOS/APTES hybrid membrane (33.61 mg g−1 with pH of 4.5 and at a temperature of 45 °C). Thermodynamic parameters were evaluated to understand the nature of adsorption process for uranium ions. The negative values of Gibbs free energy change (∆G°) and positive value of enthalpy change (∆H°) showed that the adsorption of uranium onto both of the electrospun and casting hybrid membranes was feasible, spontaneous and endothermic in studied conditions. The reusability of hybrid membranes was determined after five sorption–desorption cycles and the results showed that these membranes can be utilized extensively in industrial activities.

Removal of uranium (VI) from aqueous solution by adsorption of hematite

In this work, a new type of hyper-crosslinked phosphate-based polymer (HCPP) polymerized by bis(2-methacryloxyethyl)phosphate has been developed for uranium and rare earth element (REE) extraction in an aqueous solution. The influence of the pH value, contact time, initial concentration, temperature, and competing ions on uranium adsorption of HCPP is investigated in detail. HCPP exhibits a maximum uranium adsorption capacity of up to 800 mg g-1 at pH = 6.0 and excellent selectivity toward uranium adsorption over coexisting ions, because of the high affinity between HCPP and uranium ions and dense phosphate groups on the backbone. It also demonstrates high adsorption performance in both simulated seawater with a high salt concentration and a real nuclear industrial effluent. Besides, the crosslinked network structure of HCPP endows this polymer with high chemical stability and reusability. Furthermore, the adsorption mechanism is probed by energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared measurements. It is confirmed that the adsorption of uranium on the adsorbent originates from the interaction between phosphate groups and uranium ions. Meanwhile, HCPP also displays high REE adsorption capacities. This work indicates that the phosphate-based HCPP could be utilized as a promising adsorbent for the effective removal of uranium and REEs from aqueous solution.

A porous adsorbent was prepared from leather waste by activation with alkali. The adsorbent, alkali-activated leather waste (AALW), was applied to adsorb uranium(VI) and characterized by scanning electron microscopy, energy-dispersive X-ray detection, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The influence of the pH, initial uranium(VI) concentration, temperature, and contact time on the adsorption of uranium(VI) was systematically investigated. The adsorption of uranium(VI) on AALW obeyed the Langmuir isotherm model and was attributed to ion exchange and complexation coordination. Thermodynamic and kinetic studies showed that the adsorption process was spontaneous and endothermic, and it reached adsorption equilibrium in 360 min. Moreover, the selective adsorption of uranium(VI) from an aqueous solution containing coexisting ions and adsorption of trace uranium(VI) from a simulated high-salinity environment showed that AALW had not only a strong affinity but a high se...

Efficiency and mechanism of adsorption of low concentration uranium in water by extracellular polymeric substances

Synthesis of a mesoporous aluminophosphate

THE synthesis of inorganic mesoporous materials using ionic surfactant template molecules was first reported in 19921,2, and surfactant-mediated synthesis has since been used to form a variety of mesoporous materials3–8. Such materials could find application in catalysis, membrane and separation technology, and molecular engineering. Previous syntheses have used low surfactant concen-trations, and the templating mechanism (which is still controversial) is thought to be a cooperative process involving the interaction of inorganic ions with discrete surfactant aggregates1,2,5,9. Here we report the templating of silica mesostructures from ordered liquid-crystalline mesophases: the resulting silica phase, with pores of ∼3 nm diameter, is a cast of the organic mesophase. As the phase diagram of the surfactant/silica/water system at high surfactant concentration is similar to the (known) phase diagram of surfactant/water alone, this approach should introduce an element of predictability into the synthesis of mesoporous materials.

Synthesis of a hydrotalcite-like compound from oil shale ash and its application in uranium removal